Fine structural analysis of neuronal connections within the cat cochelear nucleus will be continued in correlated light (LM) and electron microscopic (EM) material from normal and experimental cats. The region under study, the "octopus cell area" (OCA), unusual for its single morphological cell type and for its heavy cochlear input via cytologically di ferent synapses, can be physically isolated from fixed brains for correlated structural study by several methods: The proposed work includes continued studies of seral thin sections for EM to determinethat two cytologically different (hetermorphic) synapses do arise from single auditory fibers. Both lesion studies and horseradish-peroxidase (HRP) injections have already excluded the superior olivary complex as a major source of input to OCA; future work will use these methods to study possible inputs from either higher auditory nuclei or from intrinsic neurons in the cochlear nucleus. Some neurocytochemical studies are proposed for LM and EM study, including fluorescence work and initial enzyme cytochemistry. This investigation may provie the structural basis for functional analysis of lower mammalian auditory systems. It may yield new possibilities of synaptic organization in mammalian central nervus system. BIBLIOGRAPHIC REFERENCES: Kane, E.S.C. l975 Neuroanatomical clues to peripheral locomotor control in brine shrimp (Artemia salina). Amer. J. Anat., l43: 485-500. Kane, E.S.C. l975 Superior olivary inputs to cat cochlear nucleus. Society for Neuroscience Abstracts, p.39.